The adjuvant activity of synthetic N-acetylmuramyl-dipeptide: evidence of initial target cells for the adjuvant activity

Human beta casein fragment (54-59) modulates M. bovis BCG survival and basic transcription factor 3 (BTF3) expression in THP-1 cell line

Immunostimulatory peptides potentiate the immune system of the host and are being used as a viable adjunct to established therapeutic modalities in treatment of cancer and microbial infections. Several peptides derived from milk protein have been reported to induce immunostimulatory activity. Human β -casein fragment (54–59), natural sequence peptide (NS) carrying the Val-Glu-Pro-Ile-Pro-Tyr amino acid residues, was reported to activate the macrophages and impart potent immunostimulatory activity. In present study, we found that this peptide increases the clearance of M. bovis BCG from THP-1 cell line in vitro. The key biomolecules, involved in the clearance of BCG from macrophage like, nitric oxide, pro-inflammatory cytokines and chemokines, were not found to be significantly altered after peptide treatment in comparison to the untreated control. Using proteomic approach we found that BTF3a, an isoform of the Basic Transcription Factor, BTF3, was down regulated in THP-1 cell line after peptide treatment. This was reconfirmed by real time RT-PCR and western blotting. We report the BTF3a as a novel target of this hexapeptide. Based on the earlier findings and the results from the present studies, we suggest that the down regulation of BTF3a following the peptide treatment may augment the M. bovis BCG mediated apoptosis resulting in enhanced clearance of M. bovis BCG from THP-1 cell line.

Well-defined and potent liposomal hepatitis B vaccines adjuvanted with lipophilic MDP derivatives

The characterization of immunological cascades of the innate immune system activated by invariant molecular structures termed as pathogen-associated molecular patterns recognized by pattern recognition receptors of macrophages and dendritic cells, have allowed the elucidation of the mechanisms underlying the immunomodulatory properties of adjuvants. Thus, adjuvant-active lipophilic analogues of N-acetyl muramyl dipeptide (MDP) were incorporated in liposomal hepatitis B surface antigen (HBsAg) formulations. The immunoreactivity of the formulations was evaluated by measuring anti-HBs, immunoglobulin G (IgG), and isotype antibody titer and compared with alum-adsorbed HBsAg formulation. The formulations were also evaluated for cell-mediated immune response by HBsAg-specific proliferation of splenocytes and simultaneous estimation of cytokines (interleukin-4 [IL-4], interferon-gamma [IFN-gamma]). Results indicate that the serum IgG and anti-HBs titer obtained after intramuscular administration of liposomal muramyl tripeptide-phosphatidylethanolamine (MTP-PE) and liposomal N-acetylmuramyl-l-alanyl-d-isoglutamine-glycerol dipalmitate (MDP-GDP) antigenic formulations were significantly higher. The incorporation of MTP-PE on the liposomal HBsAg increased the stimulation index (SI) four to five times as compared to plain HBsAg solution, and it also induced significantly higher Th1 cellular immune response with a predominant IFN-gamma level. So it is the novel effective and potentially safe approach in which liposomes act as delivery vehicles for hepatitis B viral antigen to antigen-presenting cells and is ornamented with a biological response modifier that could activate these target cells to enhance the antigen presentation to T lymphocytes.

FROM THE CLINICAL EDITOR

In this study, adjuvant-active lipophilic analogues on N-acetyl muramyl dipeptide (MDP) were incorporated in liposomal hepatitis B surface antigen (HBsAg) formulations. The immunoreactivity of the formulations was evaluated and found effective, leading to a potentially enhanced immune response against the delivered antigen.

Efficacy of human beta-casein fragment (54-59) and its synthetic analogue compound 89/215 against Leishmania donovani in hamsters

The characteristic feature of visceral leishmaniasis (VL) is the profound impairment of immune system of the infected host, which contributes significantly to the partial success of antileishmanial chemotherapy. Since in VL, cure is the combinatorial effect of drug and immune status of the host, the rationale approach towards antileishmanial chemotherapy would be to potentiate the immune functioning of the host to extract desired results. Towards this direction several rationally designed analogues of human beta-casein fragment (54-59) were evaluated for their ability to stimulate the non-specific resistance in hamsters against Leishmania donovani infection. By virtue of being derived from the food protein casein derivatives may be devoid of unwanted side effects associated with the substances of microbial origin, e.g. muramyl dipeptide (MDP). Out of this one peptide Val-Glu-Gly-Ile-Pro-Tyr (compound 89/215) had been reported to have such activity. In this communication, the prophylactic and therapeutic efficacy of the peptide along with its natural sequence has been evaluated in detail against experimental VL in hamsters. Their use as an adjunct to chemotherapy was also explored. Human beta-casein fragment, compound 89/215 and MDP were tested in vivo at various dose levels wherein compound 89/215 showed superiority over MDP at 3 mg/kg x 2 given intraperitoneally (i.p.). Compound 89/215 sensitized peritoneal macrophages acquired considerable resistance and only 24% of the cells were found infected in comparison to control peritoneal macrophages where 76.4% of the cells were found infected. Similarly, the efficacy of sodium antimony gluconate (SAG) in hamsters pretreated with compound 89/215 enhanced significantly (P < 0.001). This peptide also exhibited considerably good therapeutic efficacy when evaluated either alone or in combination with SAG in established infection of L. donovani.

N-acetylglucosamine-containing muramyl peptides directly affect macrophages

In this study flow cytometry was used to show that macrophages were the major population of murine peritoneal exudate cells (MPEC), increasing Ia expression upon treatment with N-acetylglucosaminyl-beta 1-4-N-acetylmuramyl-alanyl-D-isoglutamine (GMDP). Modulation of Ia expression resulted from direct action of GMDP on macrophages, rather than from effect of cytokines released by T-cells. The effect of GMDP on two populations of macrophages, namely, slow and rapid responding, was studied in detail. Rapid responding cells were represented by Ia-positive macrophages: GMDP augmented their Ia expression. In contrast, slow responding subpopulation was represented by initially Ia-negative macrophages, in which GMDP induced de novo synthesis of Ia-antigens. The ability to induce Ia expression was also characteristic for other adjuvant-active N-acetylglucosamine-containing muramyl peptides (GMPs). Macrophages were shown to engulf GMPs by endocytosis. Activation of macrophages by GMDP resulted in an increase in their phagocytic activity.

Species dependency of in vitro macrophage activation by bacterial peptidoglycans

The effect of various bacterial cell wall components on in vitro biological function of murine peritoneal exudate macrophages was evaluated. We examined four different parameters of metabolic activity and monokine secretion. Peritoneal exudate macrophages from rats and guinea pigs, all of the strains tested, were stimulated by whole bacterial cell wall preparations, purified bacterial cell wall peptidoglucans, its water-soluble peptidolglycan fragments, muramyl dipeptides and amphipathic substances. Murine peritoneal exudate macrophages were activated by amphipathic substances of gram-positive bacteria. However, macrophages from mice, irrespective of strains, were not stimulated in the in vitro assay systems by purified bacterial cell wall peptidoglycan, water-soluble bacterial peptidoglycan fragments or muramyl dipeptides. These results suggest that macrophage activation by bacterial peptidoglycan in vitro is animal species specific.

Lack of response of murine peritoneal macrophages to in vitro activation by muramyl dipeptide (MDP). I. Macrophage activation by MDP is species dependent

Peritoneal exudate macrophages from mice, rats, and guinea pigs were assessed using six different parameters of macrophage activation to determine whether the cells were stimulated under similar experimental conditions. Peritoneal exudate macrophages from mice, irrespective of strain, were far less responsive to a variety of in vitro stimulatory effects of N-acetylmuramyl-L-alanyl-D-isoglutamine than those from rats or guinea pigs, while no significant differences were noted with the reactivity to stimulation by endotoxic lipopolysaccharide. We conclude that macrophage activation by MDP in vitro is species dependent.

Enhancement of immunoglobulin G responses in mice against hepatitis B virus surface antigen, influenza virus hemagglutinin vaccine, and tetanus toxoid by 6-O-acylated muramyl dipeptides

The adjuvant activity of chemically synthesized 6-O-acylated muramyl dipeptides (MDP) was tested in aqueous form. The activity was assessed by determining immunoglobulin G (IgG) titers in sera of mice immunized with hepatitis B virus surface antigen, influenza virus hemagglutinin (HA) vaccine, or tetanus toxoid with an enzyme-linked immunosorbent assay. Administration of 6-O-acyl-MDP analogs with antigens induced marked enhancement of primary and secondary IgG antibody responses and maintained high antibody levels for at least 7 weeks. Among the analogs tested, an MDP methyl ester carrying a 6-O-3-hexadecanoyl-oxytetradecanoyl group (compound 309) exhibited the most intensive adjuvant activity. Its activity was stronger than that of 6-O-2-tetradecylhexadecanoyl (B3O)-MDP used as a positive control. However, accumulation of peritoneal cells and activation of peritoneal macrophages by compound 309 was weaker than that by 6-O-B30-MDP, suggesting that 309 as an immunoadjuvant is more suitable for vaccination in terms of its stronger enhancement of antibody formation and lower induction of inflammatory response than 6-O-B30-MDP.

A systemic study of enhancement of host defense processes against bacterial infection

A sequence of studies over more than two decades has identified a variety of host defense abnormalities that may contribute to clinical infection in high risk and/or badly injured patients. Clearly, animal studies set the stage for our clinical applications and suggest that a variety of so-called non-specific host defense stimulants may indeed correct many of these abnormalities and promote the ultimate control of surgical infections.

Augmentation of immune responses by a muramyl dipeptide analog, MDP-Lys(L18)

The effects of N2-(N-acetyl-muramyl-L-alanyl-D-isoglutamyl)-N6-stearoyl-L-lysine (MDP-Lys(L18], a muramyl dipeptide (MDP) analog, on the immune responses in mice were studied. MDP-Lys(L18) augmented the mitogenic responses of splenic lymphocytes to phytohemagglutinin (PHA) and lipopolysaccharide (LPS) at 0.1-10 micrograms/ml, and antibody formation to sheep red blood cell (SRBC) in normal and immunosuppressed mice, and to dinitrophenyl (DNP)-Ficoll. In addition, MDP-Lys(L18) potentiated polyclonal B cell activation both in vivo and in vitro. It was also found that MDP-Lys(L18) augmented the cellular immune responses, such as mixed lymphocyte reaction (MLR) and delayed type hypersensitivity (DTH). These effects of MDP-Lys(L18) were more potent than those of MDP. These findings may be attributed to the interleukin 1 (IL-1)-inducing activity of MDP-Lys(L18).

Muramyl dipeptide induced augmentation of the proliferative response of thymocytes to phytohemagglutinin

N-Acetylmuramyl-L-alanyl-D-isoglutamine (MDP) augmented the proliferative response of thymocytes to phytohemagglutinin (PHA). The augmenting effect of MDP disappeared by passage of glass-nonadherent thymocytes through Sephadex G-10 (G-10) column or by removal of low density cells by the Ficoll-Conray gradient centrifugation. The diminished augmenting effects of MDP on the proliferative response of glass-nonadherent-G-10 nonadherent thymocytes was restored by the addition of the G-10 adherent cells. When G-10 adherent cell fraction was extensively depleted of macrophages by glass adherence and EA-rosetting, it was found that neither the macrophage-depleted G-10 adherent cell fraction nor the macrophage fraction supported by itself the proliferative response of G-10 nonadherent thymocytes. However, addition of macrophage fraction together with the macrophage-depleted G-10 adherent cells did support the proliferation of G-10 nonadherent thymocytes. It was further shown that peritoneal exudate macrophages could be substituted for thymic macrophage fraction. These results suggested that both the G-10 adherent-glass nonadherent cells and macrophages were essential for the MDP-induced augmentation of the proliferative response of thymocytes to PHA and these cells exerted different accessory roles in this response.

Synergistic effect of glucantime and a liposome-encapsulated muramyl dipeptide analog in therapy of experimental visceral leishmaniasis

A regimen of immunostimulation with 6-0-stearoyl-N-acetylmuramyl-L-alpha-aminobutyryl-D-isoglutamine, a lipophilic analog of muramyl dipeptide, combined with antimonial drug therapy was evaluated in the treatment of visceral leishmaniasis of mice and hamsters. The combined treatment was found to be more effective in the elimination of Leishmania donovani amastigotes from infected tissue macrophages than was either of the two treatments applied individually. In mice, it was found that immunostimulation of animals prophylactically, therapeutically, or both enhanced the effects of the antimonial drug (Glucantime) administered more than 1 week after a challenge of BALB/c and C57BL/6 mice. The superiority of the combined treatment of the parasite infection was demonstrable in both short-term (14 days) and long-term (40 to 45 days) infections of the two inbred strains of mice. The combined therapy was also effective in preventing the lethal course of leishmaniasis in hamsters which succumb to disseminated disease in the absence of therapeutic intervention. The efficacy of this dual approach to the therapy of disseminated leishmaniasis of experimental animals holds promise for similar application in the treatment of similarly afflicted human populations.

Restoration and stimulation of the in vitro immune response of B cells to sheep erythrocytes by interleukins and muramyl dipeptide (MDP)

MDP, a synthetic muramyl dipeptide, is capable of increasing the primary in vitro antibody response, to sheep erythrocytes, of purified B cells restored with a monokine and helper T cell factors, including Interleukin 2 and the late-acting T cell replacing factor (TRF). First, the possibility that the adjuvanticity of MDP could be due to the elaboration of Interleukin 1, caused by its effect on macrophages, was excluded. In addition, a kinetic study showed that the effect of MDP was greater when added later, concomitantly with or one day after the helper T cell factors. Therefore, it appears that MDP acts directly on B cells, in a late stage of their differentiation to antibody-producing cells.

In vitro immune response to sheep erythrocytes in macrophage depleted cultures. Restoration with interleukine 1 or a monokine from resident macrophages and stimulation by N-acetyl-muramyl-L-alanyl-D-isoglutamine (MDP)

The involvement of macrophages in the adjuvanticity of N-acetyl-muramyl-L-alanyl-D-isoglutamine (MDP) has been examined. The stimulation of the in vitro primary immune response to sheep red blood cells (SRBC) has been studied, because it is known that macrophages cooperate through the mediation of soluble compounds for the induction of the anti-SRBC response. The cultures depleted of macrophages by passing spleen cells on Sephadex G-10 were unable to give any response to SRBC. Their immune responsiveness was fully restored by the addition of either Interleukine 1 (IL 1) obtained from P388D1 cells or a factor able to replace macrophages (FRM) obtained from resident peritoneal macrophages. MDP alone, at any dose, was unable to induce any response in such macrophage depleted cultures, but it was able to enhance the antibody response of these cultures reconstituted with monokines, with the same characteristics in dose effect and timing dependence than in whole spleen cells.

Stimulation of chemiluminescence by synthetic muramyl dipeptide and analogs

The effect on respiratory burst of murine splenic cells after in vitro exposure to synthetic muramyl dipeptide (MDP) and 6-O-acyl and quinonyl derivatives was studied at an early phase of interaction by luminol-dependent chemiluminescence (CL) in response to stimulation by zymosan. The MDP molecule enhanced CL, but the degree of CL response varied with the kinds of fatty acids introduced in the chemical structure of synthetic glycopeptide analogs. A 6-O-acyl derivative possessing an alpha-branched fatty acid chain, B30-MDP, stimulated maximum levels of CL activity. High CL responses were obtained with L8-MDP having a short chain of linear fatty acids and with QS-10-MDP-66 containing a ubiquinone compound. CL was also stimulated by MDP and its analogs in the spleen cells of nude mice lacking mature T lymphocytes, but the extent of stimulation was decreased compared with that of normal spleen cells.

Enhancement of antigen-specific suppression by muramyl dipeptide

The effect of the synthetic adjuvant MDP (N-acetyl-muramyl-L-alanyl-D-isoglu-tamine) on the generation of antigen-specific suppression was investigated. Suppression of the anti-bovine serum albumin response, which was achieved by intravenous administration of a peptic fragment of the antigen, was greatly enhanced by simultaneous administration of MDP. Induction of suppression by a combination of bovine serum albumin fragments and MDP was found to be antigen specific and appeared to occur via the generation of antigen-specific suppressor T cells.

Muramyl dipeptides: prospect for cancer treatments and immunostimulation

The immunopharmacological activities of bacterial cell walls and muramyl peptides were collected in table form with a comprehensive literature. The past and present studies emphasizing the host-defense enhancing activities of muramyl peptides for antitumor immunotherapy were surveyed along three possible approaches: 1) the nonspecific enhancement of natural defense ability of host against tumor cells themselves; 2) the enhancement of nonspecific resistance of host to microbial infections which are frequently encountered and difficult to treat in the advanced stage of tumor patients; and 3) the stimulation of immunity against tumor-specific or tumor-associated immunogens. Finally, the prospects of successful antitumor immunotherapy with muramyl peptides and their derivatives was discussed.

Adjuvant activity of purified peptidoglycan of Listeria monocytogenes in mice and guinea pigs

The immunological properties of peptidoglycan (L-PG) purified from the cell wall skeleton (L-CWS) of Listeria monocytogenes strain EGD were investigated and compared with the properties of L-CWS. L-PG consisted of alanine, glutamic acid, alpha, epsilon-diaminopimelic acid, muramic acid, and glucosamine. L-PG showed potent adjuvant activities for circulating antibody formation and development of delayed-type hypersensitivity to bacterial alpha-amylase in vivo and for the primary immune response to sheep erythrocytes in vitro, as well as L-CWS. Both L-PG and L-CWS enhanced the generation of cell-mediated cytotoxicity in allogeneic mice and activated thioglycolate-elicited peritoneal macrophages and macrophage cell line RAW 264 to kill tumor target cells in vitro. We also found that L-PG acted on normal spleen cells as a mitogen. Both L-PG and L-CWS had tumor (Meth A)-suppressive and -regressive activities in syngeneic mice. Our results suggest that the L-PG moiety retains the adjuvant and antitumor activities of L-CWS.

Stimulatory effect of N-acetyl Muramyl dipeptide in vivo: proliferation of bone marrow progenitor cells in mice

The effects of single and multiple injections of N-acetyl muramyl dipeptide (MDP) on peripheral leukocytes, colony-forming cells (i.e., bone marrow granulocyte-macrophage progenitor cells), and the humoral immune response (to bovine serum albumin) were investigated in mice. Whereas low doses of MDP (0.1 to 1 mg/kg) provoked lymphocytosis, larger doses (10 mg/kg upward) resulted in lymphocytopenia and an increase in the number of young stab neutrophils and monocytes. MDP induced a dose-dependent increase in the number of bone-marrow macrophage progenitor cells, the maximum being reached by a dose around 10 mg/kg. A 50% increase in the maximum effect was produced by a dose around 0.1 mg/kg. The higher the dose, the longer the increase in these progenitor cells persisted. MDP mediated a dose-dependent antibody response to small amounts of bovine serum albumin, correlating with the proliferation of progenitor cells.

The immunology of mycobacterial infections

Mycobacteria are endowed with substances that profoundly affect the immune system. Leprosy and tuberculosis exemplify broad spectra of useful and detrimental immune responses of mycobacterial infections that range from intense potentiation to severe specific adn nonspecific suppression of humoral and cellular immune elements. The cellular hypersensitivity induced by mycobacteria serves as a classical model for the analysis of specific and nonspecific immune mechanisms. Mycobacterial disease are prevalent worldwide and rank among the most important bacterial diseases. The kaleidoscope of immunologic events induced by injected mycobacteria and during infections will be reviewed from the standpoint of pathogenesis, pathology, in vitro and in vivo effects on cellular and humoral arms of the immune response, diagnosis, classification, potentiation and suppression.

Lack of immunostimulatory effect of N-acetyl muramyl-L-alanyl-D-isoglutamine on selected chicken immune functions

Synthetic N-acetyl muramyl-L-alanyl-D-isoglutamine, syn. muramyl-dipeptide (MDP) was found to be immunostimulatory in several experimental animal species. In order to determine the influence of MDP on the chicken immune response, different doses (0.05-0.2 mg) of this compound were administered to 6-week old chickens, and cellular as well as humoral immune functions were tested. Neither the immune response against sheep red blood cells or Newcastle disease virus (strain Hitchner B 1), nor the ability to reject skin grafts, or to react in the delayed hypersensitivity (tuberculin) test, were affected significantly under the experimental conditions employed. This study reveals little evidence for parallels between the ability of the chicken immune system and the immune system of other animal species examined so far, to develop enhanced immune reactions under the influence of MDP.

Macrophage activation by muramyl dipeptide (MDP) without lymphocyte participation

An increase in the numbers of spread macrophages caused by macrophage stimulants was found to be a very sensitive measure for macrophage activation. Muramyl dipeptide (MDP), bacterial lipopolysaccharide (LPS), and lymphokines were found to activate macrophages dose-dependently as measured by this parameter. Macrophage activation by MDP was strictly dependent on its adjuvant-active stereochemically specific structures. Macrophage activation by MDP and LPS occurred without lymphocyte participation. It is suggested that LPS also activates macrophages via lymphocytes.

Macrophage activation by muramyl dipeptide as measured by macrophage spreading and attachment

A synthetic bacterial cell wall constituent, muramyl dipeptide (MDP), was found to induce the enhancement of macrophge spreading and attachment on glass or plastic surfaces. Macrophages exposed to bacterial lipopolysaccharide or lymphokine-containing cell supernatants showed similar enhancement. This finding supports the view that MDP activates macrophages. MDP was also found to enhance the viability of macrophages but to inhibit 3H-thymidine incorporation by macrophages.

Increased production of superoxide anion by macrophages exposed in vitro to muramyl dipeptide or lipopolysaccharide

After in vitro exposure to lipopolysaccharide (LPS) or muramyl dipeptide (MDP), cultured resident mouse peritoneal macrophages were primed to display enhanced generation of superoxide anion (O2-) in response to stimulation by phorbol myristate acetate (PMA) or opsonized zymosan. Priming with LPS (1 microgram/ml) produced a sevenfold enhancement of PMA-stimulated O2- generation; priming was detected within 30 min and persisted for at least 4 d. Exposure to MDP (1 muM) primed the macrophages to double their O2- release; the response was first observed after 4 h and persisted for at least 3 d. The priming response was not observed with stereoisomers of MDP, which are inactive as adjuvants. LPS and MDP appeared to work directly on the macrophages rather than indirectly by interacting with adherent lymphocytes: (a) Addition of nonadherent cell populations that contained lymphocytes had no effect on the response. (b) The response was normal with cells from nude mice, which lack mature T lymphocytes. (c) Macrophages from C3H/HeJ mice, whose B lymphocytes fail to respond to LPS, were weak in their response to priming LPS; the addition of normal (C3Heb/FeJ) nonadherent cells had no effect on this weak response. (d) The macrophage-like cell line J774.1 also showed enhanced O2--generating capacity after a 4-h exposure to LPS or MDP. The O2--generating capacity of macrophages primed with LPS in vitro was equivalent to that previously observed with cells elicited in vivo by injection of LPS or activated by infection with Bacille Calmette-Guérin. The data suggest that previous exposure to bacterial products could prime macrophages to respond with increased production of toxic oxygen metabolites on contact with invading microorganisms or tumor cells.